I think what got him, was that he was expecting that safety to stay on the receiver, he expected movement from him to adjust to Andre's motion.

He comes to the LoS & the defense he sees suggests man. Chancellor was about 7 or 8 yards off the LoS over the TE in the slot. When Andre motions inside the slot, Schaub looking out the corner of his eye expects the safety to come to the LoS to get a hand on Andre, or prevent OD from crossing inside & providing a natural pick for Andre.

So I think (no way to really tell & Matt will never say) Matt saw the safety start his motion to the LoS & then lost track of him. He never saw Chancellor open up towards the line, completely turning his back on Andre. If Schaub saw that, he would have recognized the blitz... no way he couldn't. Then he would have checked to the run.

Watching that play, you can't see the run lanes open suggesting we would have picked up the 4 yards. The TE approaches the MIKE like he's going to block, then breaks off into a route at the last minute. But if Matt would have signaled run, that would have been a good block & a big seam.

After reading your WCO instruction manual, I think I have a better understanding of the system. The audibles. It's all in the snap count. One word means the play called in the huddle, another means the back up play. So this, "Can't audible once the motion is called." is Kubiak falling on the sword. That motion is supposed to help Matt make the call. He just mis-read it.

The point of putting a man in motion is to see what the defense does. If you can't audible after seeing what the defense does, why bother?

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“Of course, if one ignores contradictory observations, one can claim to have an ‘elegant’ or ‘robust’ theory. But it isn’t science.”
— Halton Arp